1. Field of the Invention
The present invention relates generally to a visual travel route indicating apparatus for use in a vehicle. More particularly, the invention relates to a visual travel route indicating apparatus, for use in an automotive vehicle or the like, which is specifically designed to visually display combined information on a current status of travel of the vehicle, such as a current location, a path of travel, a travel direction, etc.
2. Description of Relevant Art
In attempts to prevent the driver of an automotive vehicle or the like from losing his way while driving such as at night or in unfamiliar surroundings away from his desired route of travel, there have been developed a variety of devices which are designed to provide continuously or discretely a due current position or similar information on the vehicle by way of an indication panel or display screen including a related road map or the like disposed at the driver's seat so that he may receive a suitable ready guidance relating to the vehicle's current status of travel with respect to a desired course of travel.
In the conventional travel route indicating devices for application as described above, a current travel distance of a vehicle is detected in accordance with its travel speed and time by a distance detecting unit, a current bearing and a current amount of azimuthal deviation of the vehicle are detected by a rate type bearing detecting unit adapted to detect a possible angular velocity as produced about the axis of yawing of the vehicle, a current location of the vehicle along its travel route is obtained from an arithmetic operation on the thus-detected location data, and the results of such operation are indicated by way of spot information, changing from time to time as the vehicle progresses in its travel, on a display which visually indicates a suitable road map of routes on which the vehicle is to travel.
In the conventional devices described hereinabove, a terrestrial magnetism compass and a gyroscope are most commonly employed as the means for detecting a bearing or azimuthal deviation. However, because the device employing a terrestrial magnetism compass is susceptible to sources of magnetic disturbance such as steel rails, an iron bridge, etc., it is inevitable that the azimuthal deviation detected by such type of devices suffers from a substantial deviation in the indication of a travel path of a vehicle encountering such disturbance. Moreover, it is also impractical to install such devices in consideration of the vehicle's own magnetism environment. On the other hand, such a device employing a gyroscope cannot be relieved from an accumulated error in detection mainly because of its own drift which may be produced in operation. With such aforesaid devices, therefore, it is very possible that spot information showing a current location of the vehicle on the display would deviate from a predetermined course of travel, because of such errors in detection, to such an extent that such spot information would indicate an erroneous location of the vehicle on the display screen which may include a map of complicated and crowded roads and streets. As a consequence, therefore, it is very difficult, if not impossible, for the driver of the vehicle to determine whether the displayed information on the monitor screen of the display unit is erroneous or if the vehicle is actually travelling away from the desired course, thus resulting in substantial ambiguity.
The present invention effectively overcomes the aforesaid inconveniences and disadvantages attendant the conventional travel route indication apparatus.